Laboratory hammer mill



w. H. ROSS ET AL LABORATORY HAMMER MILL Filed Jan. 18, 1943 2 Sheets-Sheet 1 gwuwwbm ROSS IE. 8. SHIPLEY J.- F. MULLINS J O- HARDESTY Dec. 25, 1945. H, QSS A 2,391,480

LABORATORY HAMMER MILL Filed Jan. 18, 1943 2 Sheets-Sheet 2 Patented Dec. 25, 1945 RATORY HAMMER mar. William H. Ross, Elias s. Shlpley and Joseph F.

Mullins, Washington, D.

0., and John 0.

Hardesty, Hyattsvllle,. Md., asslgnors to the United States of America as represented by the Secretary of Agriculture Application January "18, 1943, Serial No. 472,682- 3 Claims. (01. 241-100) (Granted under the act 01' March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the pay- -ment to us of any royalty thereon.

This invention relates to an improved laboratory hammer mill for the dry grinding of samples of fertilizers and like materials for chemical analysis.

About 50 percent of the average mixed fertilizer of a few years ago'would pass a 40-mesh sieve. A mixture of this kind contains suflicient finelydivided material to more than fill the interstices between thelarger particles. Such a mixture exhibits little tendency to segregate in its original form and still less when ground for analysis. Within recent years there has been a tendency to increase the particle size of. superphosphate and other components of fertilizer mixtures with a. view to improving the drillability of the mixture. Little or no segregation is likely to take place in mixtures of this kind in the original form if the size of the particles is approximately the same. However, when mixtures containing a large proportion of coarse particles are ground for analysis-to pass through l-mm. openings in a sieve, as recommended in the oflicial procedure of the Association of Oflicial Agricultural Chemin through the screw feeder in the mill. The

materials for which they are designed. The high speed of rotationof the hammers develops a strong current of air through these mills. This is an advantagewhen grinding any considerable quantity of a material as it tends to keep the mill cool. This current of air is a disadvantage, however, when grinding small samples for analysis. Some mills of this type are provided with a cloth tube which connects the outlet of the mill with the container in which the ground material is to be collected. The cloth tube permits the escape of the surplus air taken amount of fine dust which escapesthrough openings between attached fittings or through the mesh of the cloth tube in the initial stages of the grinding operation is insignificant when large quantities of material are being ground but, when small samples of /2 to 2 pounds are being ground for analysis, the loss of any dust becomes impor- 1 tant to the true determination of the chemical ists, the proportion of relatively'coarse to finelydivided material passing the sieve may be such as to cause segregation when the sample is handled or agitated.

It has recently been found, however, that good results are obtained in the analysis of the ordinary type of mixed fertilizers that have been ground to pass a -mesh Tyler standard screen scale sieve. The diameter of the'opening in this sieve is 0.417 millimeter. A recommendation was accordingly adopted by the association that dry mixed fertilizers be ground for analysis to pass a 35-mesh Tyler standard sieve in place of a 1-mm. sieve.

Fertilizer mixtures as a rule are diflicult to grind and any regulation that requires finer grinding would add considerably to the cost of preparing fertilizer samples for analysis if such grinding is to be done with the laboratory grinding equipment now on the market. This equipment includes such devices as the mortar and pestle, bucking board, Wiley mill, and various types of plate, roller and hammer mills. The electrically driven screen hammer mills are very effective for grinding the quantity and type of composition of the sample. This is particularly evident when one ingredient of a fertilizer mixture shatters easily by impact of the hammers and is converted into a very fine dust while other ingredients of the same mixture are not reduced to such'fineness. When theplantnutrient under consideration for analysis is mostly present in the finer material, its loss by dusting causes considerable discrepancy between chemical results and the actual nutrient value of the mixture.

Most fertilizers when finely divided are inclined tobe sticky. This is due in part to the tendency of some fertilizer materials to become more hygroscopic with decrease in particle size. When a small sample is ground in a mill of the type previously employed, it is often found diflicult to recover all the ground sample due to losses by dusting, to packing of the material in crevices and roughened surfaces on the interior of the mill, and to the tendency of the material to stick to the cloth tube through which the surplus air escapes.

The laboratory grinding devices now on the market have the further disadvantages that the material being ground is exposed to the air for a relatively long period, as usually happens when thesample is ground in a mortar and pestle, or to a strong current of air for a shorter period, as occurs when it is ground in mills of the hammer type. Many fertilizer materials have the property of rapidly absorbing moisture from the air on a Furthermore, hammer mills used. in the past have consisted of a large number of detachable parts which are diflicult to clean and cumbersome to handle. To dismantle and reassemble such mills for a large number of small analytical samples is time-consuming and laborious.

An object of our invention, therefore, is to provide a laboratory hammer mill that is capable of grinding fertilizers and like materials in a much shorter time than other devices on the market.

- A further object of this invention is to provide a laboratory hammer mill that is adapted to grinding fertilizers and like materials without loss or gain of moisture during the operation.

A further object of this invention is to provide a laboratory hammer mill that is capable of grinding a fertilizer or like material without appreciable loss of any portion of the sample by dust- Another object of our invention is to provide means for rapidly sealing and unsealing a laboratory hammer mill, thereby facilitating the bandling of a large number of laboratory samples without loss of significant quantities of sample, and the cleaning of the mill in a minimum period of time after each grinding operation.

A still further object of the invention is to provide a laboratory hammer mill that can be readily and quickly cleaned, thereby avoiding any loss of material by adherence to any portion of the mill or contamination of any subsequent material entering the mill.

With the foregoing and other objects in view, this invention consists of such novel features of construction, combination and arrangement of parts as will be hereinafter more fully described and illustrated in the accompanying drawings and claims.

' In describing the invention in detail, reference will be had to the accompanying drawings,

wherein like characters designate like and corresponding parts throughout the several views, and in which:

Figure 1 is a vertical section of the improved hammer mill.

Figure 2 is a vertical section ofthe improved mill taken on line AA of Figure 1 with the motor shown in elevation.

Figure 3 is a right side elevation of the improved mill with door open 90 and the support funnel-shaped adapter II below the slotted outlet-opening 5 of the mill housing; a screw cap l2 attached to the bottom of the adapter II; and a bottle 13 of standard construction that can be screwed into the screw cap l2 of the funnelshaped adapter ll.

The sample to be ground is fed into hopper l0 and is carried by means of the screw conveyor 9, which is inclined at about and operated ,by handle l4 or by motor (not shown), through the center of the closed hinged door 3 into the mill housing 2 where the hammer assembly 4 operating at 8000 to 10,000 R; PPM. accomplishes pulverization of the particles and ejection of the ground material through the removable screen 6, which is held in place flush with the interior surface of the housing 2 and above the outletopening 5 by means of slots I5 situated at the edges of outlet-opening 5. The pulverized material then passes through the removable funnelshaped adapter I i which is sealed air-tight to the housing 2 by means .of a gasket l6 and thumb screws ll. The pulverized material then passes into the receiving container i3 which is sealed by means of thumb screws 2| operates in con--' junction with an adjustable hinge 22 and dovefunnel-shaped adapter shown in Figures 2 and 3.

Referring more particularly to the drawings, the improved hammer mill of this invention come prises a base I, whereby the mill proper may be mounted on a table or other support; a onepiece cylindrical mill housing 2 constructed of, or lined with, stainless steel or other corrosiveresistant material, and which with the hinged door 3 serves as a housing for the hammer assembly 4; a slotted outletopening 5 in the bottom of the cylindrical housing; a removable screen 6 for covering the slotted outlet-opening 5; a one-half H. P. motor I on the shaft 8 on which is mounted directly the hammer assembly 4; a

spiral feed-screw conveyor 9 mounted on the hinged door 3-of the mill housing; a feed hopper I0 attached to the screw conveyor 9; a removable tall assembly, as shown in Figure 4, to give equal pressure around the circumference of gasket 23 and seal the hinged door 3 to the face of housing 2.

The hinged door 3 is attached to a dovetail 24 by means of a hinge pin 25. The dove-tail 24 slides in groove block 26 attached to the circumference of the housing 2 by means of screws 2! and is held in sliding position by means of L'- shaped retainer plate 28 secured to dove-tail 24 by clamp-screw 29 and. operating against a rubber cushion 30. Slot 3| in L-shaped retainer plate 28 allows adjustment of the L-shaped retainer plate 28 against the rubber cushion 30 so that when the door 3 is clamped in position on the face of housing 2 the dove-tail 24 and L- shaped retainer plate 28 slide forward exerting a pressure on rubber cushion 30 which causes the gasket 23 on hinged door 3 to be pulled tightly against the face of housing 2.

While the improvements herein disclosed have been described with relation to fertilizers, it is to be understood that the novel features of construction, and the combination and arrangement of means for obtaining these desirable results with small-analytical samples, may be applied to any materials that can be satisfactorily subjected to pulverization in hammer mills.

We have found that, in grinding small samples for analysis, it is neither necessary nor expedient to have a flow of air through the mill, and that it is highly important to have the mill sealed airtight at all places except at the feed inlet.

We have also found that the high speed rotation of the hammers in our mill creates an initial current of air which is blocked by the truly sealable means, causing a vacuum to be established at the center of rotation of the hammers and a corresponding pressure on the interior walls of the mill at and beyond the periphery of the hammers which prevents further passage of air unless the seals are broken. Thus, our mill is positively sealed against pressure from within. when it is in operation.

I Comparative tests made on various mills and grinders conducted on a-large number oi representative samples of fertilizer materials and mixv tures showed that the above-described mill required an averageof 37.2 percent less time for handlin Va-DOlli-ld samples than the 'most efll-;

cient of the other hammer millstested. Furth'ermore, an average of 99.34 percent of the sample was recovered as compared to 97.33- percent for the most eillcient of the other hammer mills;

' This, in addition to the fact that the samples did not change appreciably in moisture. content during the grinding operation in our mill. is a remarkable improvement in the grinding of analytical samples for analysis. 6

Having thus described our invention, we claim: a

1. In a hammer mill having a plurality. of rotatable hammers enclosed in a housing and air- I impermeable. discharge-collecting means at-' tached to said housing by an air-tight connection, a scalable door forming a side of said housing parallel'tothe plane of rotation of said hamfmers, hinging means attached-to said door, said hinging means including-a dovetail tenon member slidingly received'by a complementary mortice member on said housing. an adjustable L-shaped which are adjacent said dovetail member and complementary mortice member, means to secure adjustably said dovetail member'to the retainer plate, yieldable means positioned between the re-' tainer plate and said complementary mortice member and sealing means positioned between positioned at the outlet of said housing, means for forming an air-tight connectionbetween the discharge member at one opening and the housing at its outlet, an air-impermeable receptacle and airtight means to attach said receptacle to the discharge member at its other opening, whereby the entire device is adapted to withstand. pressure from within.

3. In a hammer mill having a plurality ofrrotatable hammers enclosed, in a housing and airimpermeable discharge-collecting means attached to said housing. by an air-tight connecretainer'plate therespective arms of which are.

adjacent" said dovetail member and complementary mortice member, means to secure adjustably said dovetail member to the retainer plate, yieldable means positioned between the re-- tainer plate and said complementary mortice member and sealing means positioned between said doorand the adjacent edges of the housing,

whereby an air-tight connection with said housgin is'eirected when said door is in closed posi- -t'ion, fasteningmeans for securing said'door in closed positioman inlet to said housing in said 0 ad acent 'to the axis oi rotation of saidhammers. and substantially air-tight'means for introducing material into the housing through said inlet.

- 2. In ahammermillhavinga plurality o f roair-tight means for introducing'material into said housingfa scalable door forming a side of said housing parallel to the plane of rotation of said hammers, hinging means attached to said door,

said hinging means including a dovetail te'non member slidinslsj received by a complementary mortice member on said housingsah adjustable- L-shaped retainer plate the respective'arms-of" tion, a sealable door forming a side of said housingparallel to the plane of rotation of said hammers, hinging means attached to said door, said hingingv means including a sliding member at such angle to the edge-of the annular wall of-' said housing as to oppose the motion of-said door slidingly received by a complementary mor-.

tice member on said housing, an adjustable L- shaped retainer plate the respective arms of which are adjacent said sliding member and complementary mortice member? means to secure adjustably said sliding member to the retainer plate, yieldable means positioned between the tatable hammers enclosed in a housing having'anl outlet at the bottom thereof and substantially 45 closed position, an inlet to said housing in said retainer plate andsaid complementary mortice member designed to resist the closing motion of the door, and sealing means positioned between c said door and the adjacent edges oi the housing, whereby an air-tight connection with said housing is effected when said door is in a closed position, fastening means for securing said door in 1 door adjacent to the axis of rotation ofsaid hammers. and substantially air-tight means for ini n.- noss.

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